A known transformation mode for thermosetting resins is a molding under compression, consisting in mold forming the material (for example an unsaturated polyester resin reinforced with glass fibers and including a filler, a catalyst and a release or stripping agent) under a conjugated action of a pressure of 50 to 200 bars and a temperature brought to about 110.degree. C.-160.degree. C.
Heating of the material is then obtained by heat transfer between the mold working surfaces and the work piece. Since this heating is effected by conduction, homogeneity of the heating is difficult to control. The time during which the temperature is increasing is in fact imposed by various factors, amongst which is the geometry of the work piece.
The mold is heated by a network of electric resistances or by heat conveying fluid circulation channels.
The arrangement of the fluid distribution channels is difficult to make for obtaining a uniform heating. Temperature differences are therefore found between various points of the working surfaces, resulting in aspect faults which are incompatible with a required quality for the finished piece.
Moreover, since the heat transfer by conduction is not homogeneous in volume, it is therefore the surface of the work piece which is first brought to temperature prior to the core of the work-piece. The subsequent polymerization or curing obtained is therefore not uniform, and it results therefrom, very often, inner stresses causing deformations which can appear a long time after the piece has been made.
The present invention provides a new method and a new device solving the hereabove exposed difficulties.